Such a coupling is in particular designed to be used in a network of underwater hydrocarbon transport pipes. The pipe network is submerged in an expanse of water, in particular at a significant depth.
This network is for example designed to connect different wellheads to each other, or different pipeline end terminations (PLET) in order to collect the fluid taken from the different wells of an underwater oilfield and bring it to the surface through at least one riser.
In some cases, in particular at great depths, the temperatures of the expanse of water in which the pipe network is submerged can be low, for example several degrees Celsius.
In that case, the fluids transported through the pipe network may become very viscous. This reduces the flow rate of the fluid extracted outside the facility.
In the worst-case scenario, hydrate plugs may form and completely block the recovery of fluid through part of the facility.
In order to offset this problem, it is known to heat the fluid flowing in the pipes, either by passing electric current directly through the metal tube guiding the fluid, or by providing an electric heating line positioned between an inner metal tube containing the fluid and an outer metal tube. The latter configuration is designated by the term “Electrical Tracing Heated Pipe-In-Pipe” (ETH-PIP).
The electric heating lines are relatively easy to install in the annular space between the inner tube and the outer tube of a linear rigid pipe element. A layer of high-quality thermally insulating material, for example formed by an aerogel, is also introduced into the annular space, to provide good thermal insulation between the outside of the pipe element and the fluid flowing in the pipe element.
In some configurations, a T coupling, made up of a single metal shell, is mounted between three linear pipe elements to hydraulically connect those elements. The T coupling is respectively connected to a first double-shell pipe element and a second double-shall pipe element each containing an electric heating line.
Then, a water resistant insulating material is poured around the metal shell of the coupling. An electric connecting line is also positioned in the expanse of water around the coupling to electrically couple the electric heating lines of the pipe elements mounted on the coupling.
Such a coupling is not fully satisfactory. The insulating material surrounding the coupling provides thermal insulation lower than that of an insulating material contained in a double shell of a linear pipe element. A cold point may therefore appear at the coupling.
Furthermore, the electric connecting line is connected to the heating lines in a wet environment, directly in the expanse of water. A deterioration of the electrical connection, or even short circuits, may appear.